A forming method of a resistive memory device is provided. The forming method includes: conducting a forming procedure to apply a forming voltage to the resistive memory device such that the resistive memory device changes from a high resistive state to a low resistive state and measuring a first current of the resistive memory device; performing a thermal step on the resistive memory device and measuring a second current of the resistive memory device; and comparing the second current to the first current and determining to apply a first voltage signal or a second voltage signal to the resistive memory device or to finish the forming procedure according to a comparison result of the first current and the second current. In addition, a memory storage apparatus including a resistive memory device is also provided.